1. Field of the Invention
The present invention relates to a production system which is used for an expert system and more particularly to a method and system of a production system for performing high speed inference by the conflict resolution strategy designation method, the high speed inference method on the basis of the conflict resolution strategy, or the high inference method.
2. Description of the Prior Art
An expert system allows a computer in which expert knowledge is incorporated to make high level judgment and work which are generally carried out by an expert. A production system has been developed as an effective tool for constructing this expert system.
Knowledge which is used by the production system includes a rule in the "if condition then conclusion" format consisting of the condition and conclusion which express expert knowledge and actual data which expresses facts and conditions and they are stored and inferred in the rule base and actual database.
The inference engine of the production system infers by the syllogism by applying the condition evaluation process, conflict resolution process, and conclusion evaluation process repeatedly for each rule in the rule base and each actual data in the actual database. The condition evaluation process evaluates the condition of each rule in the rule base and each actual data in the actual database (called condition evaluation) and obtains all sets (instances) of rules in which the conditions are satisfied and of actual data which satisfy the conditions so as to generate a conflict set (a set of instances). The conflict resolution process selects an instance from the conflict set on the basis of the conflict resolution strategy which is an evaluation standard. The conclusion evaluation process executes the conclusion described in the rule of the selected instance. According to the conventional production system, a conflict resolution strategy is selected from a plurality of strategies which are provided beforehand. Therefore, the selection degree of freedom of a user is limited.
As to the high speed technique of inference in the production system, an evaluation method relating to a conflict resolution strategy where the rule description order is the priority order is indicated, for example, in SIG-ARC, 89-ARC-75, 75-3 (1989); Information Processing Society of Japan. By this method, the number of comparisons of rule conditions and actual data for designation of an instance is reduced. However, since histories of instance candidates which are checked already are used, a lot of memories for storing histories and a lot of time for searching for histories are required. As to selection of a conflict resolution strategy, the aforementioned method is used.
According to the above prior art, the condition evaluation process of the production system saves the combination [page 3] status (candidate histories) of rules which are already checked and actual data and avoids double check using it. Therefore, although the number of item checks of the condition evaluation process is reduced, a lot of time and memories are required for the processing for avoiding double check.
Since the degree of freedom of strategies which can be designated by a user is limited, the last instance cannot be specified often.